ORLANDO, Fla. 
AFL-CIO leaders said Tuesday their decision to oppose Arkansas Sen. Blanche Lincoln's re-election bid should send a powerful message to other Democrats who fall out of step with unions.

Officials at the nation's largest labor federation call the move part of a more aggressive posture to make sure labor's support is not taken for granted.

"The time has come to draw a line in the sand," said Gerald McEntee, president of the American Federation of State, County and Municipal Employees. "Regardless of your party affiliation, if you're not with us, you are against us."

Union leaders also voiced public frustration with the Obama administration during their annual winter meeting in Florida. The AFL-CIO's executive council passed a resolution Tuesday saying it is "appalled" at the comments of President Barack Obama and Education Secretary Arne Duncan condoning the mass firings of an entire faculty at a poorly performing high school in Rhode Island.

The resolution came a day after labor officials privately complained to Vice President Joe Biden about how the White House is responding to labor's priorities. The developments could mean additional trouble for Democrats in the midterm elections since union members are among the most reliably Democratic voters and spend millions to boost turnout.

McEntee, who heads the AFL-CIO's political committee, said unions soured on Lincoln after she declined to support a the "card check" bill that would make it easier for workers to form unions and helped kill support for a public option in President Obama's health care overhaul plan. Lincoln also voted against union lawyer Craig Becker to become a member of the National Labor Relations Board.

At least three unions have already pledged $1 million each to helping Arkansas Lt. Gov. Bill Halter in his primary challenge to Lincoln.

Spokeswoman Katie Laning Niebaum said Lincoln has a lifetime voting record of backing the AFL-CIO 82 percent of the time.

"While she hasn't agreed with organized labor on every issue, she has always given their priorities a fair hearing and careful consideration," Niebaum said. She noted that Halter has yet to publicly reveal his position on card check.

AFL-CIO political director Karen Ackerman warned that other Democrats who won labor's support in the past may find that they are not endorsed or endorsed without labor spending any campaign resources.

"Those who have not proven themselves will not get the support of the labor movement," she said.

In a change this year, the federation will focus more on promoting issues and less on backing specific candidates. Its signature issue is the push for more spending to create new jobs.

To win labor's support, candidates "will have to be very bold in showing they support jobs programs," Ackerman said.

AFL-CIO President Richard Trumka wants Congress to pass a "financial speculation tax" on securities trading that could raise some $400 billion for new jobs, particularly in infrastructure. He plans to trumpet the jobs campaign at dozens of rallies across the country, though it is not clear whether the proposal has any support from the White House.